The importance of oil transportation in the maritime industry has increased in recent years due to increased oil and gas production. According to technical and financial aspects, on hydrocarbon transfer methods, the pipelines are the best option for the transfer of oil and gas in the maritime industry. High temperature and high pressure in the pipeline can lead to the buckling. Buckling can either be in the direction of vertical (upheaval) and horizontally (lateral). The uncertainty in the buckling parameters of the pipeline increases error in the uplift and the effective axial compressive force calculation. The existence of these errors in the pipeline design is costly for the project. So reducing the errors can be very important. This paper presents the reliability analyses for studying and quantifying the variation of the reliability index (β) with the main parameters involved during the upheaval buckling of submarine buried pipes caused by high temperature and pressure conditions (HTHP). In this paper, uncertainty is considered in the geometric parameters of the pipeline. PDF and reliability index (β) can be determined by FORM and other. FORM, FOSM and sampling methods are three main methods which are used to account the PDF and reliability index (β). This research shows that among these three methods, for a fixed state, the sampling method has the lowest beta and the highest probability of buckle, which has a higher accuracy than the other methods. For soil cover with a thickness of more than 1000, it is worth noting that by increasing the thickness of the soil cover, more force is required for the upheaval buckling in the pipeline.
Subsea pipelines due to the reduction of transfer costs and expedite the offshore operations is one of the all-purpose structures in marine industries. Subsea pipelines are exposed to a variety of hazards, including corrosion and fatigue Etc. Free span exacerbates the fatigue required parameters due to a phenomenon called the Vortex Induced Vibration (VIV). In this research, the influence of the span's length on the free span subsea pipeline has been reviewed with ABAQUS standard code. In this study the previous result has been expanded. The results of the VIV fatigue life are extensible to all of the depth. Achieved Results indicate that the fatigue life of the pipeline even in the worst condition is much higher than the required amount that it represents the upstream design of DNV-RP-F105. In this study the backrest pipeline has been investigated and result show that the pipeline under the different conditions in the backrest, by creating more vibration and displacement on one side of the pipeline reduces the fatigue life of 113 percent compared to snap. The VIV fatigue life has undergone a lot of changes due to span length changes, maximum changes occur between cable and behavioral which the amount of these changes is reduced by 75%. The free span length is another factor in VIV fatigue. VIV fatigue life will be increased by reducing the span length. As well as increasing the flow velocity that is the main factor in creating the VIV is increased fatigue. Therefore, in terms of the accuracy in the choice of the existing conditions of very high importance for the pipeline. Comparison between effect parameters in VIV fatigue life was shown that span length is the most effective parameter.
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